metamorphic
Quartzite Cobble
Metamorphosed Quartz Sandstone (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-brown surface due to weathering, likely white or pink internally; Luster: Dull/earthy on surface, vitreous inside; Crystal Structure: Granoblastic (interlocking quartz grains); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- Dull/earthy on surface, vitreous inside
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-brown surface due to weathering, likely white or pink internally; Luster: Dull/earthy on surface, vitreous inside; Crystal Structure: Granoblastic (interlocking quartz grains); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause original quartz grains to recrystallize into a dense, interlocking mosaic of crystals. The rounded shape indicates significant mechanical weathering and transport by water or glacial action during the Pleistocene or Holocene epochs.
Uses & applications
Used primarily in heavy construction, road ballast, and as a decorative landscaping stone. High-purity quartzite is used as a source of silica for glass manufacturing and silicon metal production.
Geological facts
Quartzite is so tough that it often survives multiple cycles of erosion, outlasting softer rocks. It is frequently found as 'glacial erratics'—rocks transported by ice sheets hundreds of miles from their original source.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and high resistance to chemical weathering. It lacks the foliation (layering) found in schist or gneiss. Commonly found in riverbeds, glacial tills, and mountainous metamorphic terranes.
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